The present invention relates to the exhaust systems of gas engine driven heat pumps. In particular, the invention relates to an apparatus and method for the removal and treatment of corrosive condensate, and dispersion of remaining exhaust gases, produced in the exhaust streams of gas engine heat pumps.
It is well known that heat pump systems are selectively operable in heating and cooling modes of operation, respectively, to transfer heat into or remove heat from the living spaces of a building. In gas engine driven heat pump systems, an internal combustion engine prime mover produces refrigerant vapor compression, and selectively reversible refrigerant connections convey the refrigerant between an outdoor heat exchanger and indoor heat exchanger.
Ambient outside air has been used as the heat source in the heating or heat pumping mode, and as a heat sink for the cooling mode. In the heating mode, the outside heat exchanger is operating as an evaporator drawing heat from the ambient air heat source. During the heating mode, when the ambient air is at lower temperatures, i.e., near the freezing temperature of the moisture in the air, the problem of frozen condensate on the outdoor refrigerant heat exchanger becomes a serious one. As the moisture collects on the outside heat exchanger, the build up of frost acts as an insulator, reducing heat exchange at the outdoor heat exchanger surfaces, reducing system thermal efficiency, and reducing heat pumping effectiveness.
In some gas engine driven heat pump systems the engine exhaust is introduced into a fan compartment which includes the outdoor heat exchanger coil of the heat pump. Natural gas engines generate exhaust gas which contains water vapor, hydrocarbons, CO, CO.sub.2, NO.sub.x, and SO.sub.x as byproducts of combustion. Dispersion of the exhaust gas and even mixing with the airflow drawn through the outdoor coil is desirable from an aesthetic standpoint to disperse and mask the exhaust gas odor, and engine noise, and to dilute exhaust gas moisture. In the heating mode, the outdoor heat exchanger may also recover some heat from the engine exhaust.
However, the water vapor present in the exhaust stream can exacerbate the build up of frost on fan compartment and outdoor heat exchanger surfaces, reducing heat pump operating efficiency. Localized icing can result if the exhaust gases impinge directly on the fan motor, blade or fan compartment grille. Moreover, during various operating modes, under certain conditions the water vapor can condense and combine with the NO.sub.x and SO.sub.x to produce an acidic condensate. The acidic condensate consisting mainly of HNO.sub.3 and H.sub.2 SO.sub.4 accelerates corrosion on the exhaust system, the fan and fan compartment surfaces, and the outdoor heat exchanger. If drained from the fan compartment, the acidic condensate may have undesirable environmental effects, particularly on nearby vegetation.
One method of minimizing exhaust condensate is to insulate the exhaust hardware and maintain high exhaust temperature. However, such insulation adds to cost and size of the system. Further, the maintenance of high exhaust temperatures is incompatible with the use of an exhaust heat recuperator, which is preferred in the exhaust systems of gas engine driven heat pump systems to recover exhaust heat and improve overall heat pump system efficiency. The cooling of exhaust gases which results from use of a recuperator makes elimination of exhaust condensate under all operating conditions nearly impossible.
Accordingly, the need exists to provide for improved dispersion and mixing of engine exhaust gases, and proper removal and disposal of exhaust gas condensate, in order to reduce engine exhaust odor and noise, minimize icing, frosting and corrosion of the exhaust system, fan, fan compartment surfaces, and the outdoor heat exchanger, and to permit the use of desirable heat recovery features in gas engine driven heat pump systems.